The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention.
A decrease in stress myocardial perfusion represents an early marker reflecting the functional effects associated with abnormalities in the coronary arteries. To date, myocardial perfusion imaging (MPI) is most commonly assessed using nuclear imaging modalities. Stress cardiac magnetic resonance (CMR) is not yet widely used—particularly in the United States; however, multiple multicenter trials have demonstrated higher accuracy in detection of obstructive coronary artery disease (CAD) with CMR than with SPECT MPI. With recent hardware and software improvements, vasodilator stress CMR first-pass perfusion imaging is emerging as an attractive alternative, providing comprehensive cardiac assessment with a radiation-free approach.
Despite significant technical advances during the past decade, persistent problems have limited the widespread use of perfusion CMR. One problem is that CMR is a complex method far more dependent on the expertise of the technologist than nuclear myocardial perfusion imaging, and in general is considered to be a complicated modality for diagnosis of CAD. A major source of complexity has been the need for near-perfect ECG gating.
A second problem is that stress MRI studies are commonly associated with an artifact that makes image interpretation difficult even for experts. This image artifact is referred to as the subendocardial dark-rim artifact. In the perfusion image series, dark-rim artifacts are most pronounced when the contrast bolus first washes into the left ventricular cavity—particularly during the stress portion of the examination. The artifact lasts for a few heartbeats, and mimics true perfusion defects. Consequently, dark-rim artifacts remain a major drawback for accuracy and wide-spread adoption of perfusion MRI since they impede diagnosis of hypoperfusion in the subendocardium, which is the myocardial layer characteristically seen to have abnormality in ischemic heart disease.
Stress perfusion imaging with CMR offers the promise of providing a comprehensive cardiac examination without radiation. Its high resolution allows for distinguishing subendocardial from subepicardial hypoperfusion, something that cannot be resolved by nuclear methods. This quality of perfusion CMR could overcome the problem associated with “balanced reduction of flow” that is known to be a mechanism by which nuclear MPI can miss the most high risk forms of the disease.
In view of all of the aforementioned considerations, there is clearly a need in the art for an improved CMR perfusion technique that eliminates the need for ECG gating altogether and produces images free of the dark-rim artifact.